An analog memory element is an essential component in a number of novel computer architectures. Associative memories, neural networks and general purpose analog computers require a means for storing analog information for long periods of time. A related MOS analog memory (MAM) was disclosed in the above referenced related patent application by Reedy, Shimabukuro and Garcia and was published as "Dual Polarity Nonvolatile MOS Analogue Memory (MAM) Cell For Neural-Type Circuitry" in ELECTRONIC LETTERS, Sept. 15, 1988 Vol. 24, No. 19 pp. 1231-1232. The MAM used a pair of complementary MOSFETs to inject either holes or electrons onto the floating gate. One side effect of this approach was that large currents were noted as being required to generate the avalanche injection. A further observation was that the writing of holes also was much slower than electrons by several orders of magnitude, a consequence of which is the possibility of asymmetric writing. These observations were attributed to the structure of the original MAM and the mechanism used to write charge on and off the floating gate.
Thus, a continuing need exists in the state of the art for an integrated circuit memory element that can be increased and decreased incrementally with no knowledge of the current state (i.e., which is dual-writing-polarity), in which writing rates are similar for incrementing and decrementing, and which does not require large currents for writing.